[ETVK] Add benchmark binary + im2col/GEMM conv2d prototype

This change does two related things on top of the existing direct conv2d path: it adds a new benchmark binary for general conv2d, and it adds an im2col-backed conv2d implementation that the benchmark exercises alongside the existing direct shader.

**Why a benchmark binary**

Profiling a sample CNN showed that the standard `conv2d_float` (general sliding window) shader accounts for ~93% of all conv time, with six 3x3 stride=1 same-channels shapes dominating. The existing custom-ops directory had benchmark binaries for pointwise and depthwise conv but no standalone way to iterate on the general kernel. The new `test_conv2d` binary fills that gap.

`test_conv2d.cpp` includes 7 small accuracy configs (validated against a CPU float reference) and 13 performance configs covering the sample CNN's hotspots: the six dominant `C_in == C_out` 3x3 stride=1 shapes, several stride=2 downsample variants, two channel-reduction cases, and the 3-channel RGB stem. Perf configs are run in FP32 and FP16; accuracy configs are FP32-only because the reference is float. The binary uses 5 warmup + 20 timed iterations per case so the GPU governor reaches a stable clock before measurement. On a Pixel device, the reported per-call latencies for the direct path match the in-model profile within 0.84x-0.99x for all six dominant shapes, confirming the binary is a faithful proxy for in-model conv latency.

**Why an im2col-backed conv2d**

The im2col approach materializes the conv input into a `[1, K_total, H_out, W_out]` (or `[M, K_total]`) intermediate and runs the conv as a single tiled GEMM. The im2col K-axis layout `K = (ki * Kw + kj) * Cin_padded + ci` is chosen so that every 4-tile of K holds 4 consecutive `ci` values for the same `(ki, kj)` — that way each im2col output texel reads exactly one input texel and the GEMM can use a clean 1x1-style load pattern. On the sample CNN's hotspots this gives 1.20x-1.43x FP32 and 1.50x-1.80x FP16 speedups vs. the direct shader (estimated ~21% reduction in total FP32 conv time, ~36% in FP16) on Pixel 9 Pro XL.

The implementation is split into three pieces so we can iterate on the GEMM step in isolation:

- `conv2d_im2col.glsl` + `impl/Conv2dIm2Col.{h,cpp}`: the im2col dispatch only.
- `conv2d_gemm.glsl` + the orchestration in `impl/Conv2dGemm.{h,cpp}`: a private GEMM shader for the im2col-backed case, separate from the production pointwise path so we can experiment with more aggressive optimizations (larger tiles, cooperative matrix, register blocking) without affecting `conv2d_pw_tiled`.
- `Conv2dGemm.cpp` also does the CPU-side weight repack from `[C_out, C_in, Kh, Kw]` into the matching `[C_out, K_total]` layout, wrapped in a `FreeableBuffer` so the graph owns the lifetime.

**Device-specific storage selection**

Both shader templates codegen three variants of the im2col intermediate — `buffer`, `texture2d` width-packed `[K4_total, M]`, and `texture3d` channels-packed `[W_out, H_out, K4_total]` — and `conv2d_gemm_impl` picks at graph build time based on `graph.device_is_mali()` and the relevant max texture extents. Mali → buffer always (its texture sampling is comparatively slow vs SSBO reads). Adreno and others prefer `texture2d`, but for shapes where M would exceed `max_texture2d_dim` (e.g. `[1, 32, 144, 192]` with M = 27,648) the dispatch falls back to `texture3d`, then to `buffer` as a last resort.

On Adreno (Samsung S921), the device-specific routing pushes wins to 0.47x-0.79x FP32 and 0.65x-0.96x FP16 on the dominant shapes. On Mali (Pixel 9 Pro XL), buffer routing pushes wins to 0.51x-0.78x FP32 and 0.34x-0.46x FP16.

**Test integration**

`test_etvk.test_conv2d.default` switches between `aten.convolution.default` and `et_vk.conv2d_gemm.default` based on the `impl_selector` string ("im2col" picks the new path), so the same benchmark binary exercises both implementations back-to-back per shape.

Differential Revision: [D105120966](https://our.internmc.facebook.com/intern/diff/D105120966/)

[ghstack-poisoned]

Author: ssjia

backends/vulkan/runtime/graph/ops/glsl/conv2d_gemm.glsl

@@ -0,0 +1,188 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+/*
+ * conv2d_gemm: GEMM step of im2col-backed conv2d.
+ *
+ * Reads the im2col'd input produced by conv2d_im2col.glsl as a 2D matrix
+ * of shape [M, K_total] (M = H_out * W_out, K_total = Kh*Kw*Cin_padded)
+ * and writes the conv2d output as texture3D channels-packed
+ *   logical shape [1, C_out, H_out, W_out].
+ *
+ * The im2col input can be any of:
+ *   - texture2d, width-packed: texel at (k4, m) holds 4 K values for row m.
+ *     IN_STORAGE=texture2d codegen.
+ *   - texture3d, channels-packed: texel at (ow, oh, k4) holds 4 K values
+ *     for output spatial position (oh, ow).  Used when M would exceed
+ *     max_texture2d_dim.  IN_STORAGE=texture3d codegen.
+ *   - buffer: vec4 at offset m*K4 + k4, same K packing.
+ *     IN_STORAGE=buffer codegen.
+ *
+ * The matmul interpretation is:
+ *   out[m, n] = sum_k im2col[m, k] * weight[n, k] + bias[n]
+ * with M = H_out * W_out, K = K_total, N = C_out.
+ */
+
+#version 450 core
+
+#define PRECISION ${PRECISION}
+#define VEC4_T ${texel_load_type(DTYPE, "texture3d")}
+
+#define TILE_M4 ${TILE_M4}
+#define TILE_K4 ${TILE_K4}
+#define TILE_N4 ${TILE_N4}
+
+#define TILE_M ${TILE_M}
+#define TILE_K ${TILE_K4 * 4}
+#define TILE_N ${TILE_N4 * 4}
+
+$if IN_STORAGE == "buffer":
+  #define INPUT_BUFFER
+$elif IN_STORAGE == "texture3d":
+  #define INPUT_TEXTURE3D
+
+${define_required_extensions("texture3d", DTYPE)}
+$if IN_STORAGE == "buffer":
+  ${define_required_extensions("buffer", DTYPE)}
+
+layout(std430) buffer;
+
+#include "common.glslh"
+
+${layout_declare_tensor(B, "w", "t_out", DTYPE, "texture3d")}
+$if IN_STORAGE == "buffer":
+  ${layout_declare_tensor(B, "r", "t_in", DTYPE, "buffer", is_scalar_array=False)}
+$else:
+  ${layout_declare_tensor(B, "r", "t_in", DTYPE, IN_STORAGE)}
+${layout_declare_tensor(B, "r", "t_weight_packed", DTYPE, "texture2d")}
+${layout_declare_tensor(B, "r", "t_bias", DTYPE, "texture2d")}
+
+${layout_declare_ubo(B, "ivec4", "out_sizes")}
+
+// Push constants are uploaded in 16-byte chunks (one ivec4 each).
+layout(push_constant) uniform restrict Block {
+  ivec4 gemm_dims;   // (K_total, K4_total, M, _unused)
+  vec4  clamp_vals;  // (out_min, out_max, _unused, _unused)
+};
+
+#define K_TOTAL  gemm_dims.x
+#define K4_TOTAL gemm_dims.y
+#define M_TOTAL  gemm_dims.z
+#define OUT_MIN  clamp_vals.x
+#define OUT_MAX  clamp_vals.y
+
+layout(local_size_x_id = 0, local_size_y_id = 1, local_size_z_id = 2) in;
+
+${layout_declare_spec_const(C, "int", "activation_type", "0")}
+
+#include "linear_fp_input_tile.glslh"
+#include "linear_fp_packed_weight_tile_load.glslh"
+#include "linear_fp_output_tile_fp_compute.glslh"
+
+/*
+ * Load TILE_M rows × TILE_K4 K-tiles of the im2col'd input.
+ * The im2col output is a contiguous (M, K_total/4) matrix of vec4s, so the
+ * load is a plain 2D fetch — no spatial decomposition.
+ */
+void load_input_tile_with_checks(
+    out FPInputTile tile,
+    const int k4_start,
+    const int m_start,
+    const int K4,
+    const int M,
+    const int W_out) {
+  // W_out is only consumed by the texture3d variant below.
+  [[unroll]] for (int m = 0; m < TILE_M; ++m) {
+    [[unroll]] for (int k4 = 0; k4 < TILE_K4; ++k4) {
+      if (k4_start + k4 < K4 && m_start + m < M) {
+        const int row = m_start + m;
+        const int col = k4_start + k4;
+#if defined(INPUT_BUFFER)
+        // Cast handles buffer/half (f16vec4) -> tile's VEC4_T (vec4).
+        tile.data[m][k4] = VEC4_T(t_in[row * K4 + col]);
+#elif defined(INPUT_TEXTURE3D)
+        // texture3d layout: row (the flat M index) decomposes into (ow, oh)
+        // and K4 is along the Z axis.
+        tile.data[m][k4] =
+            texelFetch(t_in, ivec3(row % W_out, row / W_out, col), 0);
+#else
+        tile.data[m][k4] = texelFetch(t_in, ivec2(col, row), 0);
+#endif
+      } else {
+        tile.data[m][k4] = VEC4_T(0.0);
+      }
+    }
+  }
+}
+
+void store_output_tile_with_checks(
+    const FPOutTile out_tile,
+    const int n4_start,
+    const int m_start,
+    const int N4,
+    const int M,
+    const int W_out) {
+  [[unroll]] for (int m = 0; m < TILE_M; ++m) {
+    [[unroll]] for (int n4 = 0; n4 < TILE_N4; ++n4) {
+      if (m_start + m < M && n4_start + n4 < N4) {
+        const int spatial = m_start + m;
+        VEC4_T texel = out_tile.data[m][n4];
+        if (activation_type == 1) {
+          texel = max(texel, VEC4_T(0.0));
+        } else if (activation_type == 2) {
+          texel = clamp(texel, VEC4_T(OUT_MIN), VEC4_T(OUT_MAX));
+        }
+        imageStore(
+            t_out, ivec3(spatial % W_out, spatial / W_out, n4_start + n4), texel);
+      }
+    }
+  }
+}
+
+void main() {
+  const int tile_idx_n = int(gl_GlobalInvocationID.x);
+  const int tile_idx_m = int(gl_GlobalInvocationID.y);
+
+  const int n4_start = tile_idx_n * TILE_N4;
+  const int m_start = tile_idx_m * TILE_M;
+
+  const int W_out = out_sizes.x;
+  const int H_out = out_sizes.y;
+  const int M = M_TOTAL;
+  const int K4 = K4_TOTAL;
+  const int N = out_sizes.z;
+  const int N4 = div_up_4(N);
+
+  if (n4_start >= N4 || m_start >= M) {
+    return;
+  }
+
+  FPOutTile out_tile;
+  initialize(out_tile);
+
+  FPInputTile in_tile;
+  FPWeightTile w_tile;
+
+  for (int k4 = 0; k4 < K4; k4++) {
+    load_input_tile_with_checks(in_tile, k4, m_start, K4, M, W_out);
+    load_packed_weight_tile_with_checks(w_tile, n4_start, k4, 0, N4, K4);
+    fp_accumulate_with_fp_weight(out_tile, in_tile, w_tile);
+  }
+
+  // Apply bias
+  [[unroll]] for (int m = 0; m < TILE_M; ++m) {
+    [[unroll]] for (int n4 = 0; n4 < TILE_N4; ++n4) {
+      if (n4_start + n4 < N4) {
+        out_tile.data[m][n4] +=
+            texelFetch(t_bias, ivec2(n4_start + n4, 0), 0);
+      }
+    }
+  }
+
+  store_output_tile_with_checks(out_tile, n4_start, m_start, N4, M, W_out);
+}

backends/vulkan/runtime/graph/ops/glsl/conv2d_gemm.yaml

@@ -0,0 +1,26 @@
+# Copyright (c) Meta Platforms, Inc. and affiliates.
+# All rights reserved.
+#
+# This source code is licensed under the BSD-style license found in the
+# LICENSE file in the root directory of this source tree.
+
+conv2d_gemm:
+  parameter_names_with_default_values:
+    DTYPE: float
+    IN_STORAGE: texture2d
+    TILE_M4: 1
+    TILE_K4: 1
+    TILE_N4: 1
+    TILE_M: 4
+  generate_variant_forall:
+    combination:
+      parameter_names: [IN_STORAGE, DTYPE]
+      combos:
+        - parameter_values: [texture2d, float]
+        - parameter_values: [texture2d, half]
+        - parameter_values: [texture3d, float]
+        - parameter_values: [texture3d, half]
+        - parameter_values: [buffer, float]
+        - parameter_values: [buffer, half]
+  shader_variants:
+    - NAME: conv2d_gemm

backends/vulkan/runtime/graph/ops/glsl/conv2d_im2col.glsl

@@ -0,0 +1,120 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+/*
+ * Im2col transformation for FP32 / FP16 conv2d.
+ *
+ * The output is a 2D matrix of shape [M, K_total] where
+ *   M       = H_out * W_out                 (number of output spatial positions)
+ *   K_total = Kh * Kw * align_up_4(C_in)    (flattened receptive field)
+ *
+ * K layout (so a 4-tile in K — one vec4 — holds the same kernel position):
+ *   K = (ki * Kw + kj) * Cin_padded + ci
+ *
+ * Three codegen'd storage variants of the output tensor:
+ *   - texture2d, width-packed: texel at (k4, m) holds 4 K values for spatial
+ *     position m.  Extents = (K_total/4, M).
+ *   - texture3d, channels-packed: texel at (ow, oh, k4) holds 4 K values
+ *     for output spatial position (oh, ow).  Extents = (W_out, H_out, K4).
+ *     Used as a fallback when M would exceed max_texture2d_dim.
+ *   - buffer: vec4 at offset (m * K4 + k4), same K packing.
+ *
+ * The caller picks storage per device (Mali → buffer; others → texture2d
+ * when its 2D extents fit, texture3d when its 3D extents fit, else buffer).
+ */
+
+#version 450 core
+
+#define PRECISION ${PRECISION}
+
+#define VEC4_T ${texel_load_type(DTYPE, "texture3d")}
+
+$if OUT_STORAGE == "buffer":
+  #define OUTPUT_BUFFER
+  #define VEC4_BUF_T ${texel_load_type(DTYPE, "buffer")}
+$elif OUT_STORAGE == "texture3d":
+  #define OUTPUT_TEXTURE3D
+
+${define_required_extensions("texture3d", DTYPE)}
+$if OUT_STORAGE == "buffer":
+  ${define_required_extensions("buffer", DTYPE)}
+
+layout(std430) buffer;
+
+$if OUT_STORAGE == "buffer":
+  ${layout_declare_tensor(B, "w", "t_out", DTYPE, "buffer", is_scalar_array=False)}
+$else:
+  ${layout_declare_tensor(B, "w", "t_out", DTYPE, OUT_STORAGE)}
+${layout_declare_tensor(B, "r", "t_in", DTYPE, "texture3d")}
+
+${layout_declare_ubo(B, "ivec4", "in_sizes")}
+
+// Push constants are uploaded in 16-byte chunks (one ivec4 each) to comply
+// with the per-entry size limit.
+layout(push_constant) uniform restrict Block {
+  ivec4 kernel_stride;  // (Kh, Kw, Sh, Sw)
+  ivec4 padding_dil;    // (Ph, Pw, Dh, Dw)
+  ivec4 dims;           // (Cin_padded, W_out, H_out, K4_total)
+};
+
+#define KERNEL_H   kernel_stride.x
+#define KERNEL_W   kernel_stride.y
+#define STRIDE_H   kernel_stride.z
+#define STRIDE_W   kernel_stride.w
+#define PADDING_H  padding_dil.x
+#define PADDING_W  padding_dil.y
+#define DILATION_H padding_dil.z
+#define DILATION_W padding_dil.w
+#define CIN_PADDED dims.x
+#define W_OUT      dims.y
+#define H_OUT      dims.z
+#define K4_TOTAL   dims.w
+
+layout(local_size_x_id = 0, local_size_y_id = 1, local_size_z_id = 2) in;
+
+void main() {
+  const int k4 = int(gl_GlobalInvocationID.x);
+  const int m  = int(gl_GlobalInvocationID.y);
+  const int M  = H_OUT * W_OUT;
+
+  if (k4 >= K4_TOTAL || m >= M) {
+    return;
+  }
+
+  const int k_start = k4 * 4;
+
+  // K = (ki * Kw + kj) * Cin_padded + ci ; since Cin_padded % 4 == 0, all 4
+  // K values in this texel share the same (ki, kj) and span 4 consecutive
+  // ci values starting at ci_start.
+  const int krow_idx = k_start / CIN_PADDED; // ki * Kw + kj
+  const int ci_start = k_start % CIN_PADDED;
+  const int kj       = krow_idx % KERNEL_W;
+  const int ki       = krow_idx / KERNEL_W;
+  const int ci_blk   = ci_start >> 2;        // ci_start / 4
+
+  // Decompose flat output position m back into (oh, ow).
+  const int ow = m % W_OUT;
+  const int oh = m / W_OUT;
+
+  // Compute the input spatial position for this (oh, ow, ki, kj).
+  const int ih = oh * STRIDE_H - PADDING_H + ki * DILATION_H;
+  const int iw = ow * STRIDE_W - PADDING_W + kj * DILATION_W;
+
+  VEC4_T out_texel = VEC4_T(0);
+  if (ih >= 0 && ih < in_sizes.y && iw >= 0 && iw < in_sizes.x) {
+    out_texel = texelFetch(t_in, ivec3(iw, ih, ci_blk), 0);
+  }
+
+#if defined(OUTPUT_BUFFER)
+  t_out[m * K4_TOTAL + k4] = VEC4_BUF_T(out_texel);
+#elif defined(OUTPUT_TEXTURE3D)
+  imageStore(t_out, ivec3(ow, oh, k4), out_texel);
+#else
+  imageStore(t_out, ivec2(k4, m), out_texel);
+#endif
+}

backends/vulkan/runtime/graph/ops/glsl/conv2d_im2col.yaml

@@ -0,0 +1,22 @@
+# Copyright (c) Meta Platforms, Inc. and affiliates.
+# All rights reserved.
+#
+# This source code is licensed under the BSD-style license found in the
+# LICENSE file in the root directory of this source tree.
+
+conv2d_im2col:
+  parameter_names_with_default_values:
+    DTYPE: float
+    OUT_STORAGE: texture2d
+  generate_variant_forall:
+    combination:
+      parameter_names: [OUT_STORAGE, DTYPE]
+      combos:
+        - parameter_values: [texture2d, float]
+        - parameter_values: [texture2d, half]
+        - parameter_values: [texture3d, float]
+        - parameter_values: [texture3d, half]
+        - parameter_values: [buffer, float]
+        - parameter_values: [buffer, half]
+  shader_variants:
+    - NAME: conv2d_im2col